The present invention is directed to a new and improved cardiac pacer lead locking mechanism, more particularly to a lead locking mechanism which is designed for mounting in a pacer neck aperture to receive and electrically connect the terminal pin of a lead connector to the electronic circuit of the pacer. More specifically, the invention is directed to a lead locking mechanism which includes a plurality of relatively movable parts, two of which are axially aligned and another of which is confined between the first two, relative axial movement of the first two parts causing operation of the confined part for the clamping of a terminal pin of a lead connector.
Conventionally, a cardiac pacer or pacemaker includes a case or can which contains a power supply in the form of a battery as well as the necessary electronic circuitry. The case further includes a neck or housing which is designed to accept a pair of lead terminals which are connected to an electrode placed in contact with or adjacent to the cardiac muscle being stimulated. The neck or housing includes a pair of spaced apertures or passageways, each of which receives a terminal pin and each of which includes some form of lead locking mechanism for clamping the pins to the pacer so as to establish electrical continuity.
Continuing efforts are being made to reduce the size of cardiac pacers or their components, bearing in mind that pacers are intended to be implanted. One area of importance with respect to size reduction is the neck portion of a pacer, and that is the area to which the present invention is directed.
It has been conventional to utilize a lead locking mechanism in association with each pacer neck aperture, which lead locking mechanism is oriented transversely or radially with respect to the aperture and to the terminal pin to be clamped. Among the components used in such a locking mechanism is a clamping set screw which radially or transversely engages the longitudinal axis of the terminal pin and which is mounted within and accessible through an aperture communicating with a side surface of the pacer neck in order to permit application of a tool for adjustment of the set screw. A separate, frictionally held seal is inserted in the outermost end portion of the set screw aperture to prevent body fluid intrusion during the implanted condition of the pacer. The transverse relationship of these types of conventional lead locking mechanisms adds to the thickness of the pacer neck as dictated by the length of the set screw, screw block and frictionally held seal. Additionally, the frictionally held seal presents a potential problem by raising the possibility of its becoming loose from or popping out of the aperture in which it is inserted. In other words, the seal is not always as positively held as might be desired.
The present invention permits substantial reduction in the thickness of the neck portion of a cardiac pacer and also provides positive clamping of a seal in the lead terminal aperture of the neck to prevent body fluid intrusion. Reduction in pacer neck thickness is accomplished by axial or longitudinal alignment of the various parts of the lead locking mechanism in the pacer neck aperture. This improved lead locking mechanism consists basically of interacting component parts plus a seal, the components being in the form of annular members, two of which are threadedly advanceable and retractable relative to one another in coaxial alignment, and another of which is confined between the first two parts to be acted upon to radially contract or expand in clamping or releasing the terminal pin of a lead connector. The mechanism further functions to hold the seal within the pacer neck aperture in a positive manner even while the lead locking mechanism itself is being adjusted to clamp or release a terminal pin, thereby not only effectively and continuously sealing the pacer neck aperture but also preventing the popping out of the seal during and following implantation of the pacer.
All of the foregoing is generally accomplished within the confines of the pacer neck aperture itself. Typically included is the presence of only a slight enlargement of a relatively short portion of the pacer neck aperture. A chamber is formed in which the lead locking mechanism is positioned. This slight enlargement is oriented in an axial or longitudinal direction relative to the aperture, thereby permitting a substantial reduction in the thickness of the pacer neck. Such reduction typically approaches 50 percent, for example, reducing the width of a conventional pacer neck from 10 mm. to approximately 5 or 6 mm.
It will be seen that the subject invention provides a number of substantial advantages over existing lead locking mechanism designs and pacer neck configurations. Reduction of pacer neck thickness is, of course, an important advantage as described above. An additional advantage resides in the in-line operation of the lead locking mechanism and simultaneous insertion and holding of the terminal pin, these two functions being accomplished coaxially and in axially opposed directions thereby adding to the efficiency of assembly during implantation of the cardiac pacer. Still a further advantage, as referred to above, is the controlled holding and positioning of the seal at all times during clamping of the lead, thus eliminating any additional necessary step to seal the neck aperture. Simplicity of design constitutes an important advantage. Still further, an efficient and positive electrical connection is obtained and maintained. The lack of design complexity provides long life advantages. Other advantages will become apparent from the following description of preferred embodiment of the invention.